1. Technical Field
The present invention relates generally to semiconductor devices and in particular to electrostatic discharge protection devices. Still more particularly, the present invention relates to a method for fabricating a low trigger voltage silicon controlled rectifier and thick field device for use in electrostatic discharge protection devices.
2. Description of the Related Art
Electrostatic discharge (ESD) phenomena commonly result from pulses of high voltage (typically, several kilovolts), moderate current (a few amperes) and short duration (on the order of 100 nanoseconds) generated by a variety of sources such as human bodies, electric fields generated by machinery, and the like.
ESD effects are a common problem in integrated circuit (IC) electronics and are particularly troublesome in complimentary metal oxide semiconductor (CMOS) devices which have particularly thin gate oxides and very short channel devices. Such structures typically can withstand only a few tens of volts. An ESD pulse conducted through a CMOS IC can induce oxide rupture and device or interconnect burnout. An ESD pulse can also induce a "latch-up " condition in thick field devices.
ESD problems can be abated somewhat by including appropriate anti-static protection on the circuit boards on which the ICs are installed; however, the ICs still are susceptible to ESD before and during the circuit board fabrication process. A general personnel awareness of ESD problems and counter measures such as electrically grounded bracelets and the like reduce risks in this phase of the IC life span; however, it is at best a partial solution. Therefore, it is desirable to include ESD protection circuitry within the IC itself.
In fabricating ESD protection circuitry, it is desirable to produce the structures for the circuitry using as few steps as possible. The reduction in the number of steps decreases the amount of time necessary to produce a semiconductor device. Furthermore, a savings in cost and materials may be gained by reducing steps required to produce a semiconductor device. Therefore, it would be an advantage to have an improved method for fabricating ESD protection circuitry within a semiconductor substrate.